Elbow forming technologies mainly include casting and molding technologies, all of which depend on moulds. In the moulds, elbows are conformally formed by casting or hot/cold pressing techniques. Most machinery equipments and pipelines use elbows mainly for conveying various materials. Materials for elbows include cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metal and plastic materials. In building, mine, metallurgy, electric power, petroleum, coal, grain processing industries, materials are conveyed by line pressure and pipelines are subject to large pressure and severe wearing. Therefore, high overall performance requirements have been imposed on conveying pipes, in particular connecting elbows and increasing service life of elbows has become a difficulty to overcome.
Single-layer high manganese steel elbows are most commonly used elbows at present. There are also a few elbows using double layer high chromium cast iron. Single-layer high manganese steel elbows suffer poor wear resistant property, low hardness and low safety. Double-layer wear resistant elbows have high costs, better quality, excellent wear resistant property, high hardness and high safety, however their performance-to-price ratio is low. Developing a wear resistant elbow with excellent performance, low cost and good safety is a job to be done urgently in the entire industry. By searching the pipe wearing mechanism and flow mode of materials under different working conditions, simulation is conducted to find out regions that are most likely to be worn and increase the thickness of wear resistant layer or increase wear resistant property of materials in these regions for the purpose of increasing life time of the elbow as a whole, saving costs for customers and saving resources for the society.
At present, in the patent CN 2030237100 disclosed in China, a wear resistant elbow is disclosed which includes a body, and further includes a high molecular elastomer layer disposed in said body with a thickness of 3-15 mm at the middle section of said elbow and 2-10 mm at ends of said elbow. However, the wear resistant elbow suffers increased cost, high probability of being worn between the body and the high molecular elastomer layer, and high probability of peeling the high molecular layer under the washing of fluid.
In the patent CN 203286190U disclosed in China patent document, a wear resistant elbow for conveying concrete is disclosed. Said elbow is a single-layer concrete conveying elbow including an inner all and an outer wall. The arc-shaped inner surface of said outer wall is provided with a recess located on the inner surface of said outer wall at a position with largest curvature and extending towards both sides along the position. A wear resistant layer is incorporated on said recess. However, although this kind of concrete conveying wear resistant elbow includes an inner wall and an outer wall, it is actually a single-layer structure with low safety and the inner wall is formed by providing and filling a recess on the arc-shaped inner surface. In this way, its manufacturing is rather complex, and problems exist in terms of mounting fastness of inner wall and outer wall, and wear resistant effect is poor at locations other than the recess position.
In the patent CN 202561281U disclosed in China patent document, a wear resistant pipe and a wear resistant elbow pipe fitting are disclosed. The wear resistant pipe and the wear resistant elbow pipe fitting include a steel-made pipe body and a wear resistant inner lining layer of ceramic coating being provided on the inner wall of the steel-made pipe body. As an improvement, a metallic wire net is provided in the wear resistant inner lining layer of ceramic coating which is welded on the inner wall of steel-made pipe body. The wear resistant pipe and wear resistant elbow pipe fitting use a wear resistant inner lining layer of ceramic coating at inward curves, and a wear resistant inner lining layer of ceramic coating is also used in regions that does not need high wear-resistance, which results in material waste and increased costs. A metallic wire net is further embedded in the wear resistant inner lining of ceramic coating, which increases manufacturing difficulty although it can reduce drop-out of ceramics in use.
In the patent CN 104061394A disclosed in China patent document, a method for manufacturing curved pipe fittings and curved pipe fittings obtained therefrom are disclosed, including obtaining a first outer curved tubular component and a second inner curved component. Said second inner curved component is made of wear-resistant material larger than the first outer curved tubular component and has a cross section to cover at least partial inner surface of the first outer curved tubular component. The method manufactures the first outer curved tubular component into at least two components, wherein each component has a cross section that is a corresponding part of the entire tubular section of the first outer curved tubular component. The at least two components are made to be close to each other along their respective connecting edges and the second inner curved components are disposed inside and contacts at least one of the two components. The at least two components are welded to form the first outer curved tubular component and said second inner curved component is sealed inside the first outer curved tubular component. If the second inner curved component of the the curved pipe fitting adopts a semi-tube design, there will be significant problems in terms of mounting fastness of the first outer curved tubular component and the second inner curved component, and at the same time, a problem of poor wear-resistance will occur if the second inner curved component is at the extension part. If the second inner curved component adopts a complete tube design, the second inner curved component is of the same material, whereas material used for regions with low wear resistance may be relatively cheap wear resistant material, which results in wasting of material and influence on economy.